Magnetic transducer head with auxiliary means for diverting residual flux

ABSTRACT

A magnetic head is shown having auxiliary core material in a substantially unstressed condition with very low direct current coercivity and located within the working magnetic core for diverting magnetic flux due to residual magnetization of the main core of the head away from the record medium path. Crossfield magnetic heads, offset pole magnetic heads, and composite core magnetic heads with windings for different frequency ranges are also disclosed.

D United States Patent 1111 [72] Inventor Marvin Camras [56] References Cited v Glens, UNITED STATES PATENTS Eff g- 3 1966 2,895,015 7/1959 Zenel et al. 179/1002 i 1 2,230,913 2 1941 Schuller 179 1002 [45! Paemed My 2431541 11 1947 c 79100 [73] Assignee in Research Institute amras l I Chicago [11 2,538,405 1/1951 Zenner... 179/l00.2 Continuatiomimpan of application Sen No. 2,615,097 10/1952 Camras 179/1002 2,911,481 11/1959 Augustm 179/1002 835,017, Aug. 20,1959, now Patent No. 3 360 614 12/1967 C t 1 179/100 2 3,382,325damd May 7,1968anda omercie a continuation-in-part of 126,121, July 24, FOREIGN PATENTS 1961, now Patent No. 3,334,192, dated 881,343 1/1943 France 179/1002 Aug. 1, 1967. 930,545 7/1963 Great Britain 179/1002 Primary ExaminerBernard Konick Assistant ExaminerJ. Russell Goudeau [54] MAGNETIC TRANSDUCER HEAD WITH Attorney-Hill, Sherman, Meroni, Gross and Simpson AUXILIARY MEANS FOR DIVERTING RESIDUAL FLUX ABSTRACT: A magnetic head 15 shown having aux111ary core Claims 29 Drawmg Figs material in a substantially unstressed condition with very low [52] US. Cl 179/1002 direct current coercivity and located within the working mag- C, 340/ 174.1 F, 346/74 MC netic core for diverting magnetic flux due to residual mag- [51] Int. Cl Gllb 5/10, netization of the main core of the head away from the record G1 1b 5/12 medium path, Crossfield magnetic heads, offset pole magnetic Field of Search .1 179/ 100.2 heads, and composite core magnetic heads with windings for C; 340/1741 F; 346/74 MC difi'erent frequency ranges are also disclosed.

PAIENIED JUL 6 I97! SHEET 3 BF 4 INVEA '1 UR. C amrais' MAGNETIC TRANSDUCER HEAD WITH AUXILIARY MEANS FOR DIVERTING RESIDUAL FLUX CROSS-REFERENCES TO RELATED APPLICATIONS The present application is a continuation in part of my copending applications Ser. No. 835,017 filed Aug. 20, 1959 (now U.S. Pat. No. 3,382,325 issued May 7, 1968); and Ser. No. l26,l2l filed July 24, l96l (now US. Pat. No. 3,334,192 issued Aug. 1, I967); and the disclosures of each of these prior applications is hereby incorporated herein by reference.

The disclosure of my copending application Ser. No. 4l5,81l filed Mar. 12, 1954, and now abandoned, has been continued in Ser. No. 835,017, so that the broadest aspects of the present disclosure are supported by the embodiments of Ser. No.4l5,8ll.

This invention relates to magnetic transducer heads and particularly to such heads having integral means for reducing the residual magnetization thereof.

Residual magnetization in tape recorder heads may be intense enough to erase a valuable record while it is being played back. In less extreme cases the residual magnetization of the playback head causes the recorded high frequencies on the record medium to deteriorate and results in a reproduced signal with increased noise level. Further, the sensitivity of the playback head to the recorded signal is reduced when the playback head has a substantial level of residual magnetiza tion. Comparable adverse effects result during recording with a magnetized head. The adverse effects of residual magnetization are especially serious in microgap heads (a head having a gap length of 50 microinches or less) and in video recording.

Heads become magnetized by transient currents during switching of the circuits coupled with the heads; by the magnetic fields of nearby motors, loudspeakers, chokes or transformers; by peaks in the recording signal itself; by charging current in transistor input circuits; and even bystrongly magnetized tapes or the earth's magnetic field.

Heads can be demagnetized manually with an external field or by means of a decaying current through their windings, but this is troublesome and unreliable. Automatic demagnetization such as described in my copending application Ser. No. 456,192 filed May 17, 1965 (now U.S. Pat. No. 3,449,528 issued .Iune I0, 1969) is desirable but cannot guard against magnetization that occurs between dcmagnetizing intervals; also some extra parts are required which increase the cost of the recorder.

Various head constructions are described herein which are immune to residual magnetization in normal usage, giving benefits of lower noise, better sensitivity and improved high frequency response. One embodiment of the improved head constructions provides a shunt path for residual magnetism, the return path being made of a very low coercive force material such as Supermalloy in an essentially stress free condition.

Composite head configurations are illustrated which allow the use of mechanically harder materials of higher saturation density for the portion of the core that contacts the tape, which material otherwise would give unreasonably high residual magnetization. The alternative monolithic constructions are economical and give excellent response at very high frequencies.

It is therefore an important object of the present invention to provide a magnetic transducer head which is relatively immune to residual magnetization in normal usage.

It is a further object of the present invention to provide a transducer head construction which allows the use of mechanically harder materials and/or relatively high saturation density for the portion of the magnetic core that contacts the tape.

Another object of the invention is to provide an extremely economical head construction providing excellent response at very high frequencies.

A further object is to provide a head construction having a relatively large ratio of cross sectional perimeter to cross sectional area so as to minimize losses due to high frequency skin effect, thus providing a head for operation at video frequencies l megacycle per second or higher).

A still further object is to provide a magnetic head of relatively low inductance per winding turn squared.

Still another object of the invention is to provide a magnetic head wherein the inductance per winding turn squared decreases at high frequencies in the upper region of its operative bandwidth.

Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a somewhat diagrammatic elevational view of a core configuration in accordance with the present invention;

v FIG. 2 is a partial cross-sectional view taken substantially along the line "-1! of FIG. 1;

FIGS. 2A through 2N are partial cross-sectional views of ring type core constructions similar to that shown in FIG. 1

with the section line for the respective views located as indicated at Il-Il of FIG. I;

FIG. 3 is a diagram showing the magnetization curve for the main core material of the head and the magnetization curve for the auxiliary or additional material of the head which is useful in explaining the concepts of the present invention;

FIG. 4 is an elevational view showing a further core construction in accordance with the present invention;

FIG. 5 is a somewhat diagrammatic partial vertical sectional view showing a section of the core of FIG. 4 taken along the line V-V and further illustrating other parts of the .head assembly incorporating said core;

FIG. 6 is a somewhat diagrammatic partial vertical sectional view taken along the line Vl-VI of FIG. 5;

FIG. 7 is a partial horizontal sectional view taken along the line VII-VII in FIG. 6;

' FIG. 8 is a partial somewhat diagrammatic perspective view showing a further head configuration in accordance with the present invention;

FIG. 9 is a somewhat diagrammatic transverse sectional view and illustrating a keeper housing in association with the head configuration of FIG. 8;

FIG. 9A is a view similar to FIG. 9 but illustrating a different keeper housing configuration in association with the head configuration of FIG. 8;

FIG. 10 is a diagrammatic perspective view of the overall head assembly whose interior construction is represented in FIGS. 8 and 9;

FIG. 11 is a somewhat diagrammatic elevational view of a further head configuration in accordance with the present invention and showing the signal winding broken away and in section;

FIG. 12 is a diagrammatic side elevational view indicating further details of the head configuration of FIG. 11;

FIG. 13 is a somewhat diagrammatic partial top plan view of the head configuration of FIGS. ll and I2; and

FIG. 14 is a diagrammatic elevational view illustrating a further head configuration in accordance with the present invention.

It has been found that the coercive force and residual magnetization of cores after fabrication in a head are considerably higher than expected from the published values for the material itself. Investigation has shown that this is caused by stresses in the material which cannot be completely avoided in a fabricated head, since the gaps must be polished and a contact surface provided which is abraded by the tape. Also the core must be held firmly enough so that its various parts including the gap remain unchanged during its life.

FIG. 1 illustrates a core construction in accordance with the present invention including a main or working core 10 having a pair of magnetic poles II and 12 defining a gap 13. The core has a record medium path thereacross and a record medium is indicated at 14 travelling in the direction of arrow 15 successively across the poles 11 and 12 with the active magnetizable layer of the record medium- 14 in sliding contact with surfaces such as 16 of the poles l1 and 12 adjacent the gap 13. A signal winding is indicated at 17 which receives a signal current during a recording operation and which is threaded by a magnetic signal flux produced by the record medium during a playback operation. The working core is of such a cross section as to provide adequate flux carrying capacity for the maximum signal recorded on the tape 14, and the flux carrying capacity of the working core 10 is generally sufficient of itself to produce a maximum recorded signal on the tape when the signal winding 17 is energized. Accordingly, the term working core" as utilized herein refers to that range of core con figurations and cross sections which has heretofore been selected in constructing magnetic recording and/oi. playback heads from the standpoint of providing adequate signal flux carrying capacity and from the standpoint of other prior art criteria. lt is'a concept of the present invention to add further material to such a working core for the purpose of substantially reducing residual magnetization at the gap preferably by at least 50 percent which additional material would not be dictated by any of the criteria known to the prior art. The added material may also increase the flux carrying capability especially at high frequencies or may be used to reduce the head inductance and thus increase the self-resonant frequency. Such additional or auxiliary material is indicated at 20 in FIGS. 1 and 2. ln illustrated embodiment, the additional material 20 is provided by two generally C shaped parts 21 and 22 which are contiguous to the poles l1 and 12, respectively, substantially up to the region of the 13. The part 2| provides a substantially continuous low reluctance magnetic path in shunt with pole piece 11, and the part 22 acts similarly with pole piece 12. In the illustrated embodiment, the main core 10 is comprised of main core parts 25 and 26 of generally C shape having the poles 11 and 12 integral therewith defining the coupling gap 13 and having a back gap 27 between ends 28 and 29 of the core parts 25 and 26. The reluctance of the path from 28 to 11 in core part 25 and from 21a to 21b in core part 21 and back to 28 is not substantially greater'than the reluctance of the path from 28 to 11 to 12 to 29 to 28 including core parts 25and 26 and gaps 13 and 27. Preferably the reluctance of the local magnetic paths such as 28-1 1-21a-21 b-28 and 29-12-220-22b-29 including the auxiliary material is less than the reluctance of the magnetic path 28-11-1 2-29-28 which includes the gaps 13 and 27 and the main core The coercive force of the main core 10 is preferably as low as possible but may be considerably higher than the coercive force of the auxiliary core 20 because of mechanical considerations, stresses, use ofa material for core 10 with superior saturation or wearing qualities and the like.

The main core 10 is necessarily subjected to stress since the gap surfaces of the poles must be polished and since the tape contacting surfaces such as indicated at 16 in FIG. 2 are abraded by the tape 14. Also the main core 10 must be held firmly enough so that the main core parts and the gap defined thereby will remain unchanged during the life of the head.

The auxiliary core parts 21 and 22, however, are substantially or essentially unstressed and extend in parallel with the stressed main core parts 25 and 26. The auxiliary core parts 21 and 22 have an exceptionally low coercive force and are in shunt with the main or working" core parts 25 and 26 which have a higher coercive force because of the considerations that have been indicated. The gap 13 has a dimension in the direction of tape movement equal to 0.00005 inch (50 microinch) or smaller, in the example shown. With such a small gap size there is difficulty even with very small cores. With unduly small cores the construction becomes expensive and the efficiency (Q) of the head becomes smaller.

It will be noted that as illustrated in FIG. 1, preferably the signal winding 17 links the main core 10 and auxiliary core 20 in the same direction, so that the presence of the auxiliary core does not detract from the amplitude of signal flux produced at the gap during recording and does not detract from the amplitude of signal flux threading the signal winding during playback and in fact enhances the efficiency of the core.

In one advantageous form of the invention the main core 10 is of a mechanically harder material and/or having a higher saturation density than could otherwise be used, since such material would given an unreasonably high residual magnetizat-ion in the absence of the auxiliary core 20. The shunt return path provided by the auxiliary core 20 is preferably of a very low coercive force material such as Supermalloy" is an essentially stress free condition. Supermalloy has a composition 5 molybdenum, 79 percent nickel and the remainder iron and impurities and has a coercive force (measured from saturation) in its final configuration as part of the head substantially of 0.002 'oersteds, this being the value published in Ferromagnelism by Bozorth, copyright 1951, p. 871. The auxiliary core part 20 is preferably very carefully heat treated for lowest coercive force and is preferably mounted in unstressed but close fitting relation to the main core 10 as illustrated in FIGS. 1 and 2. Where necessary sufficient clearance may be provided between the main and auxiliary cores to allow for expansion, and preferably the clearance space-is filled with a nonhardening material as indicated at 30 in FIG. 2, such as silicon grease or jelly, foamed plastic, etc. for holding the auxiliary core in place. The Supermalloy or other material of the auxiliary core 20 is preferably put in place during final assembly at the time that the signal coil 17 is assembled with the head. Alternatively it may be spot welded at 21a and 22a to the main core, and carefully annealed.

The gap 13 is preferably defined by an electrically conductive gap spacer such as indicated at 32 which spacer preferably extends through the space between ends 210 and 21b of the auxiliary parts 21 and 22 and terminates below such space as shown in FIG. 1.

For general purposes the main core 10 may be of Permalloy having a composition of 4 percent molybdenum, 79 percent nickel and the remainder iron and impurities.

Where extra long life is desired, or where the head is subjected to abrasion or high tape-to-head pressures, the main core 10 may be made of a mechanically hard high permeability material as Sendust (having a composition of 5 percent aluminum, 10 percent silicon, and the remainder iron and impurities). Other mechanically hard materials for good wear resistance and sharply defined gap edges are Alfenol (an aluminum-iron alloy) and Duraperm which are available from the Hamilton Watch Co., Lancaster, Pa., U.S.A.; Silicon Steel, especially with higher silicon content such as 4 percent; and magnetic ferrites, especially single crystal and fine grain varieties which may has a glass bonded gap.

Where extra high recording fields must be generated at the gap so as to utilize tapes of exceptionally high coercivity or remanence or coating thickness, etc., without saturating the pole tips of the head (thus sacrificing resolution), the main core 10 may be made of Supermendur which has a saturation value of about 22,000 gauss (compared to about 8,700 gauss for Permalloy), or of other materials of the 50 percent cobalt, 50 percent iron type. Other high saturation materials are silicon steel (about 20,000 gauss), and 50 percent nickel-iron alloys (about 16,000 gauss). The latter is available as 4,750 alloy from Allegheny Ludlum U.S.A., Hiperik from Westinghouse U.S.A., etc.

It will be noted that many of the suggested materials are advantageous both for wear and magnetic saturation. All have a higher coercivity than unstressed Supermalloy or Permalloy.

Alfenol may comprise an iron-aluminum alloy with either 12 percent or 16 percent aluminum. Duraperm has properties generally comparable to that of Sendust. Supermendur may have a composition of 49 percent cobalt, 2 percent vanadium and the remainder iron and impurities. The 4,750 alloy may have a composition of 48 percent nickel and the remainder iron and minor constituents. Hipernik may have a composition of 50 percent nickel and the remainder iron and impurities.

By way of example, manufacturer's data gives a coercive force of 0.1 oersted for Alfenol with 12 percent aluminum, and a coercive force of 0.015 oerstcd for Alfenol with 16 percent aluminum. Supermendur is indicated to have a DC coercive force of 0.18 oersted when measured after an applied direct current field of 3 oersted. Vanadium Permendur having a composition of 1.8 percent vanadium, 49 percent cobalt and the remainder iron and impurities may also be used for the core and is stated by Bozorth, supra, to have a maximum induction 3,, of 24,000gauss, and a coercive force from saturation (c'oercivity) of2.0 oersteds.

Even where the main core is of Supermalloy, the Suermalloy cannot be in as good a magnetic condition, that is with as low a coercive force, as the auxiliary core 20 since after annealing, the top surface of the main core adjacent the gap 13 is abraded by the tape, the gap faces are mechanically polished, and the pole pieces must be firmly held in a head mount which introduces stresses from the clamping or cementing, or differential expansion.

Further, the main core 10 is preferably of an electrically lower loss material and such materials have a higher coercive force than Supermalloy.

With the head configuration shown in F1G. 1, if the head has a residual magnetization during playback (or during recording), the direction of the residual magnetization in the main core 10 may be as represented by the arrows 40 and 41. Since the main core has a higher coercive force, the magnetization of the main core will produce a residual flux in the auxiliary core having the direction indicated by the arrows 42 and 43.

Referring to FIG. 3, the magnetization curve for the main core 10 may be indicated at 50, while the magnetization curve for the auxiliary material would have a shape as indicated at 51. A curve 51a is also shown in FIG. 3 which is obtained by plotting the values of d for curve 51, but with negative values of H. With this arrangement, the intersection of the curves S0 and 51a at point 52 in the second quadrant represents the magnetic condition of the head cores in the assembly in the absence of any applied external magnetization forces.

1f the auxiliary core 20 were omitted, the residual magnetization of the main core would correspond to point 56 where the magnetization curve 50 intersects line 54, the latter representing the il /H of the magnetic path 28-1ll22928. Thus, in the absence of the auxiliary core, the main core would assume an operating condition as represented by the point 56 with the total residual flux being carried by the head gap (except for leakage); while with the auxiliary core present the main core assumes an operating condition as represented by the point 52 where the residual flux of the main core is carried by the auxiliary core, reducing the residual flux of the head gap to a negligible portion. This portion should be below the threshold where the tape is affected, preferably giving rise to gap fields below 200 oersteds.

By way of explanation of the curves S0 and 51 (FIG. 3), during energization of the signal winding 17 with a current amplitude corresponding to a maximum field of H,,,, the materials of cores 10 and 20 are cycled around the loops 50 and 51 as indicated. When the energizing field'is removed, the condition of the main core material reverts from point A to point B, while the material of auxiliary core 20 follows the path from point C to point D. Points B and D are stable only for closed rings of each material being considered. The presence of the gap at 13 in the head circuit of the main core and the corresponding gap in the auxiliary core exerts a demagnetizing influence on the material of the main core which may be depicted by a shift of the condition of the main magnetic core from point B on curve 50 to a point on curve 50 in the second quadrant. Similarly the influence of the magnetization of the main core on the material of the auxiliary core causes its magnetization to reverse and to shift from a condition as represented by point D to a condition as represented by a point on its curve in the third quadrant. Considering that the residual flux due to the main core is generally equal but opposite to the residual flux threading the auxiliary core; and that the effective magnetizing force in the two materials is equal, the magnetic condition of the main core is at point 52, and of the auxiliary core is at point 52'.

For graphical analysis it is convenient to reverse the 1 H curve of the auxiliary material as indicated by 51a in F IG. 3; in which case the magnetic condition of the materials is at the intersection of curve 51a with curve 50 at 52 in the second quadrant.

The curves of FIG. 3 are illustrative of one condition of operation. For example, under actual conditions the auxiliary material may have a steeper and narrower loop, the H may be reduced by local magnetic paths, etc.

The magnetic length of the auxiliary core is preferably shorter than that of the main core as by locating the auxiliary core on an inner radius and making it thick, this condition reducing the magnetizing force H below that of the example where equal lengths were assumed.

FlG. 2A illustrates a modified ring-type core configuration wherein the working core 10a is provided with an auxiliary core 20a corresponding to the auxiliary core 20 in FIG. 1, but the working core is further provided with additional core material as indicated at 700 and 710 which material is integral with the working core material 10a. A working core configuration including parts comparable to those at 100, 70a and 71a has been proposed in my copending application Ser. No. 126,121 filed July 24, 1961, and the disclosure of this copending application is incorporated herein by reference in its entirety. 1n the copending application, a working core was formed from a flat sheet by a die into a U-cross section and annealed after mechanical operations were completed. Such a core configuration was thus a substitute for a laminated core wherein the core parts are relatively expensive and difficult to assemble. The thickness of the sheet material used in the prior application depended on the head dimensions and on the allowable eddy current losses. For a quarter track head, 0.043 inch wide Permalloy stock 0.006 inch thick very satisfactory. Heads of this construction have been used with bias frequencies of 100 kilocycles per second and have given satisfactory response to signals of 50 kilocycles per second and higher. Thicker material is suitable for lower frequencies or larger heads. As indicated in the copending application, the width of the side flanges such as indicated at 70a and 71a in FIG. 2A may taper at the region of the gap so as to tend to concentrate flux in the path of the record medium. The corifiguration of the side flanges of the core parts adjacent the gap provides a very sensitive and convenient adjustment of the magnitude of the cross field component where a crossfield gap is also employed in the head configuration. The channel construction described in the copending application gives a selfsupporting pole piece having increased cross section by virtue of the lateral flanges, and low eddy current loss. The gap defining portions may be the same as the sheet thickness requiring no machining. The core material is in a relatively unstressed condition compared to conventional heads which are built up of laminations which are glued and clamped after annealing thus setting up stresses due to bending and to differential expansion of the glue and the laminations.

While the drawings of the prior application specifically showed a channel or U cross section, other cross sections will produce the advantages of larger flux carrying capacity wit h low eddy current loss.' For example, the core parts may have an L-cross section. A generally spiral cross section may also be formed in an initially flat sheet by bending the sheet at right angles at successively increasing intervals. In this case the sheet would be flat between successive right angle bends. The adjacent parallel portions of the sheet are suitably insulated to avoid forming a closed loop electric circuit for eddy currents.

The core parts may also have a generally O-cross section with flat sides similar to one convolution of the spiral-type cross section. The free edges of the magnetic sheet formed into an O-cross section would have a nonconductive gap therebetween to avoid a closed loop electric circuit for eddy currents having a length less than the total perimeter of the cross section.

An O-cross secton may also be formed by nesting the lateral flanges of a pair of oppositely directed strips of channel cross section. The adjacent overlapping lateral flanges of the respective strips would be insulated from each other to avoid forming a closed loop circuit for eddy currents about the perimeter of the overall O-cross section.

As a further example, a series of channel cross section strips of different size and all oriented in the same way may be nested one within the other to form a large C-cross section. A channel or C-cross section type core leg may have a solid cross section nonmagnetic filler nested therein to rigidify the leg. The filler may be nonconductive or insulated from the core leg to avoid formation of an electrically conductive loop path about the perimeter of the overall square or rectangular cross section defined by the leg and filler.

The spiral and O-cross sections just described are advantageous over conventional laminated core parts because of their case of assembly and relatively unstressed magnetic condition as finally assembled. The spiral and O-cross section core parts are advantageous over solid cross section parts of comparable flux carrying capacity because of their reduced eddy current loss. The spiral and O-cross sections provide more flux carrying capacity than a simple channel cross section, but are somewhat more difficult to fabricate and assemble. The nonmagnetic filler provides increased rigidity over the simple channel cross section core part.

FIG. 28 illustrates a working core part 10b with additional core material as indicated at 72 and 73 integral with the working core material 10b. The core configuration further includes auxiliary core material 20b formed by a series of laminations such as indicated at 74 which are electrically insulated from each other and from the core parts 10b, 72 and 73.

In FIG. 2C the working core material 100 is provided with additional material integral therewith as indicated at 76 and 77 which is integral with the working core material 10c. Each of the legs 76 and 77 has a downwardly extending portion 76a or 77a, a reverse bend portion 76b or 77b and an inturned free edge portion 760 or 77c. The portions 760 and 770 terminate in confronting free edges 76d and 77d.

In FIG. 2D the working core material 10d has auxiliary material as indicated at 78 and 79 integral therewith, and has further auxiliary material as indicated at 20d in the form of a folded sheet of low coercive force material having any of the characteristics referred to in connection with the material 20 of FIGS. 1 and 2.

In FIG. 215, the working core material 102 has essentially the same configuration as the working core material 10 and is not provided with integral additional material. Additional core material is provided as indicated at 20c in the form of a strip of magnetic material folded about the working core 10:2. The portion of the material 20:: which covers the outer surface of the working core 10e is ground away or omitted in the region of the gap so that the tape record medium 14 travels in sliding contact with the polar surface 162 of the pole He in the same way as illustrated in FIG. 1 for the pole 11. The working core material 20e includes side portions 81 and 82 integral with the portion of the material 20e covering surface of the working core 10:: (except adjacent the tape path), and the side portions 81 and 82 connect with inturned portions 83 and 84 and then with radially extending free edge portions 85 and 86. In the embodiment of FIG. 213, the auxiliary material 202 is shown as being ground away in the region of the poles of the working core 102.

In FIG. 2F, the working core lfis shown as being provided with integral auxiliary material at 90 and 91 and with further auxiliary material at 20f welded to the working core fas indicated at 92 and 93. The auxiliary core material fincludes a central portion 95 and free leg portions 96 and 97.

In FIG. 20, the working core part 10g has the same configuration as illustrated for the working core part 10 in FIGS. 1 and 2, while auxiliary material 20g is welded thereto as indicated at 101 and 102. The auxiliary material 20g includes a central portion 104 and turned leg portions 105 and 106. Secured within the auxiliary material 20g is further auxiliary material 203' welded to the central portion 104 as indicated at 108 and 109 and itself including central portion 110 and turned leg portions 111 and 112.

In FIG. 2H, the working core part 10h has integral auxiliary material as indicated at 115-120. The configuration of FIG. 2H may be extruded with the cross section illustrated and then formed into a ring shape as indicated in FIG. 1, or the portions 115-120 may be formed by milling or coining. Further aux iliary material may be provided by forming a complementary core configuration to that shown in FIG. 2H with its extensions corresponding to 115-120 extending between and intermeshed with the extensions 115-120 of the working core.

In FIG. 2I, the working core material 101' is provided with an integral flange part 122 providing auxiliary material having the characteristics discussed in connection with FIGS. 1, 2 and 2A.

In FIG. 2.], the working core material 10j is again as illustrated for the working core material 10 in FIGS. 1 and 2, and in this case is provided with auxiliary material 20 comprised of a series of laminations such as indicated at 124. The laminations of FIGS. 28 and 2] may have confronting C configurations comparable to the configuration of the auxiliary core parts 21 and 22 of FIG. 1.

In FIG. 2K, the working core part 10k is comprised of a series of laminations such as indicated at 126, each lamination having a C configuration generally conforming to the configuration of the working parts 25, 26 of FIGS. 1 and 2. The auxiliary core material 20k may be essentially identical in configuration to the auxiliary core material 20 of FIGS. 1 and 2.

In FIG. 2L, the working core material 101 has additional material integral therewith forming a configuration comparable to that which would be formed if the core parts 21 and 25 and the core parts 22 and 26 in FIG. 1 were respectively in tegral. The working core material 101 has integral extension parts 131 and 132 joined with the auxiliary material 130 by reduced portions 133 and 134 and the lateral extensions serve to provide for mounting of the core configuration to housing parts such as indicated at 136. The thinned connecting parts 133 and 134 enable the auxiliary material to absorb stresses.

In FIG. 2M, the working core material 10m is provided with integral extensions 141 and 142 and with additional material as indicated at 20m which may be in the form of two ringshaped parts having configurations such as indicated for parts 21 and 22 in FIG. 1.

In FIG. 2N, the working core material Mn is provided with integral extensions as indicated at 144 and 145, the configuration of the extensions conforming with the configuration of core parts 21 and 22 in FIG. 1, that is tapering in the region of the gap in the working core 10m so that the working core 10n provides pole tips such as indicated at 11n having a cross section essentially as indicated at 11 in FIG. 2 in the region immediately adjacent the gap in the working core 10n.

It will be apparent to those skilled in the art that the working core material in each of the embodiments which has been designated by the reference numeral 10 followed by a letter preferably has the same configuration as provided by the working core parts 25, 26 in FIG. 1. Further, the auxiliary core material integral with the working core part and the auxiliary core material designated by the reference numeral 20 followed by a letter will generally have the configuration of the auxiliary core parts 21, 22 in FIG. 1. Thus, in each case the additional material integral with the working core part will taper adjacent the gap region so that the core configuration has a cross section such as indicated at 11 in FIG. 2 in the region immediately adjacent the gap at each side of the gap. The auxiliary material thus provides generally a ring configuration but with a gap region of greater reluctance than the coupling gap such as indicated at 13 in FIG. 1 which couples the core configuration with the magnetic record medium. The magnetic record medium contacts the poles of the working core configuration adjacent the gap in the same way as indicated in FIG. 1 in each of the other embodiments.

The auxiliary material integral with the working core material in each of the embodiments may be of any of the materials heretofore mentioned for the working core part or 10a, and the auxiliary material separate from the working core parts may have any of the characteristics and be of any of the materials heretofore described with reference to the auxiliary core material or 20a.

As further embodiments of the present invention, the integral material associated with the working core material may have any of the characteristics referred to in my copending application Ser. No. 126,121 filed July 24, I96], and in this connection the auxiliary material may form part of the working core material for the purposes set forth in my copending application Ser. No. 126,121. Thus, within the broadest aspects of the present disclosure, the additional integral material may be actually required for adequate signal flux carrying capacity of the core configuration and may be dictated for adequate mechanical strength of the working core or to reduce eddy current losses and for the other purposes set forth in my copending application Ser. No. 126,12]. On the other hand, within the scope of the present disclosure, the integral additional material may be present solely for the purpose of reducing residual magnetization of the core configuration, and may not be dictated by any prior art design considerations. This latter circumstance has been specifically indicated in each of the embodiments by designating a cross section generally corresponding to the cross section shown at 10 in FIG. 2 as the working core material, and by designating the further integral material such as indicated at 70a in FIG. 2A as additional material.

In each of the embodiments, a nonhardening material has been indicated by the reference numeral followed by a letter to indicate a material corresponding to the material 30 described in connection with FIGS. 1 and 2. Each of the embodiments is specifically disclosed with the nonhardening material present for the purposes described in connection with FIG. 2, .and is also specifically disclosed with such material omitted, but preferably with the auxiliary material electrically insulated from the working core material and from additional material integral with the working core material.

In each of the embodiments, the working core material and the parts integral therewith are preferably electrically insulated where their surfaces are in adjoining relation and are also electrically insulated from any additional core material such as designated by the reference numeral 20 followed by a letter. Adjacent surfaces of the additional core material designated by the reference numeral 20 followed by a letter are also preferably electrically insulated so as to minimize eddy current losses.

The reference numeral 16 followed by a letter designates a polar surface in sliding contact with the active undersurface of the tape 14 in the same way as described with reference to the surface 16 of pole 11 in FIGS. 1 and 2.

In the various embodiments, the same reference numeral has been applied to a given part as shown in cross section and to the same part as shown in elevation so as to facilitate the reading of the drawings. Each of the FIGS. designated by the FIG. No. 2 followed by a capital letter should be considered as being a sectional view taken at a location comparable to that represented by the section line lllI in FIG. 1.

The discussion given with respect to FIG. 3 represents the preferred operation for each of the embodiments of FIGS. 2A through 2N.

Additional core configurations to some extent comparable to the illustrated embodiments are found in my copending application Ser. No. 835,017 filed Aug. 20, 1959, and each of these comparable embodiments is specifically incorporated herein by reference to illustrate certain very broad concepts included within the scope of the present disclosure.

FIGS. 4-6 illustrate an advantageous head configuration which has been built and tested and found to have a very low residual magnetization characteristic while providing low losses at highest frequencies.

In this embodiment, a working magnetic core 210 provides pole pieces 21 1 and 212 defining a gap 213 for coupling to the magnetic record medium 14 travelling in the direction of the arrow 15. As seen in FIG. 5 the pole 211 may have a tape engaging surface 216 in sliding contact with the active undersurface of the magnetizable layer 14a of the tape 14 as in the previous embodiments. The working magnetic core material 210 is provided with integral extensions 217 and 218 somewhat similar to the extensions 70a and 71a of FIG. 2A, but with inturned free edges 217a and 218a. The working core is preferably further provided with separate auxiliary material 220 comparable to the auxiliary material 20] of FIG. 21 previously described. Thus the auxiliary material is illustrated as comprising a series of electrically isolated laminations such as lamination 222. Preferably each lamination is formed of a pair of C-shaped strips comparable in configuration to the core parts 21 and 22 of FIG. 1, for example, the free edges of the strips defining a tapering configuration at the gap region as indicated at 224 and 225 in FIG. 4. As in the preceding embodiments, the main core configuration may be formed of two separate C-shaped parts such as designated by the reference numeral 231 and 232 in FIG. 4 separated to define a back gap 233. As in the previously described embodiments, the working core may comprise a rectangular cross section portion of the core parts 231 and 232 corresponding to the cross section of the pole tips 211 and 212 and corresponding to the cross section of the core parts 25 and 26 in FIG. 1. Alternatively the main core parts 231 and 232 as a whole may represent the working core for any of the purposes described in my copending application Ser. No. 126,121 as has been discussed in connection with the preceding embodiments. An electrically conductive gap spacer defining gap 213 is indicated-at 236 in FIG. 4.

The core configuration of FIG. 4 may be mounted by means of a pair of mounting blocks 241 and 242, FIG. 6 which may be of brass, bronze, or nonmagnetic stainless steel, or other nonmagnetic electrically conductive material. Each mounting block has a recess such as indicated at 2410 for receiving one of the core halves such as the half including main core part 231, FIG. 5. These recesses have a configuration so as to engage the main core parts 231 and 232 along respective limited regions such as indicated at 245 and 246 in FIG. 5. These semicircular regions may be suitably bonded to the core, for example by means of an epoxy resin having a location as diagrammatically indicated at 251 and 252 in FIG. 6 along the semicircular regions 245 and 246.

A keeper housing such as indicated at 260 may enclose the mounting blocks 241 and 242 and may have a tape engaging surface such as indicated at 260a flush with the polar surfaces such as indicated at 216, the keeper surface 260a conforming with the tape path which is indicated in FIG. 4. The keeper 260 is provided with an elongated aperture through which the poles 211 and 212 project as indicated in FIG. 5. The two mounting blocks 241 and 242 may be suitably electrically isolated at their interface, and the keeper housing will be suitably magnetically isolated from the poles 211 and 212, as by being substantially spaced therefrom by nonmagnetic material at regions such as indicated at 271 and 272 in FIG. 5.

The blocks 241 and 242 are provided with toroidal cavities 24lb and 242b so as to accommodate a toroidal winding such as indicated at 275 in FIG. 6. Instead of a single winding 275, the core configuration may have two coils linking the respective main core parts 231 and 232. In the illustrated embodiment, the keeper 260 as shown in FIG. 5 may be considered as having been ground away at the region of the poles 211 and 212 so as to show a thickness of for example 0.002 inch in FIG. 5 where its thickness elsewhere would be 0.015 inch. This configuration is shown to some extent in FIG. 6.

Referring to FIG. 7 which is a partial horizontal sectional view taken generally along the line VII-VII of FIG. 6, the epoxy resin material is designated by the reference numeral 281. It will be observed that the core parts are secured to the mounting blocks principally at the working core portion 210,

so that the side legs 217 and 218 are predominantly stress free. As indicated at 282 and 283 in FIG. 7, the clearance spaces optionally may be filled with a yieldable material such as foamed plastic as indicated at 282 and 283. Alternatively, air spaces may be left as indicated in FIG. 5.

FIGS. 8, 9 and illustrate certain important features applicable to all of the embodiments of the invention, but for convenience the features are shown applied to the embodiment of FIGS. 4-7, the same reference numerals being applied in FIGS. 8, 9 and 10 as in FIGS. 4-7.

In my copending application U.S. Ser. No. 528,934 entitled Transducer System and Method filed on Feb. 21, 1966, there is disclosed a transducer head configuration similar to that illustrated in FIGS. 8 through 10 of the present application except that in the prior disclosure a single muititurn crossfield conductor ribbon encircles both of the pole tips in the space between the pole tips and the edge of the keeper housing such as the edge indicated at 2601) defining aperture 290 in FIG. 10 of thepresent application. The disclosure of said prior application is incorporated herein by reference in its entirety, and each of the applications referred to in said copending application is also incorporated herein by reference in its entirety, these applications disclosing overall systems for utilizing the features of the present invention.

In accordance with the embodiment of FIGS. 8-10, individual electrically conductive ribbons 301 and 302 are associated with the pole pieces 211 and 212, respectively, so that the conductive ribbons may be preassembled with the associated half of the transducer head, rather than being placed over the assembled halves of the transducer head as in the prior application. Specifically in the illustrated embodiment, the conductive ribbons 301 and 302 each make approximately three turns about the associated pole piece. It will be understood, however, that the conductive ribbons may make more turns about the poles, or less numbers of turns, or only a single turn may be employed. For example in FIG. 9, approximately four turns have been illustrated in association with the pole piece 212.

FIG. 9 illustrates by means of dash lines a portion of the magnetic field configuration produced by current flow in the conductor 302. The conductor 301 and 302 may receive high frequency bias current of constant amplitude having a frequency in the megacycle range. Heating of the head core by the conductors 301 and 302 (when energized with alternating current) increases the permeability of the gap region of the head and reduces its residual magnetization. It will be noted that the fields indicated in FIG. 9 provide a gradient in the transverse direction with respect to the width of the head core with the most intense crossfield component near the lateral edges of the poles 211 and 212. With such a cross field bias configuration, the parameters may be adjusted to give optimum short wavelength recording near the central portion of the record medium channel coupled to the head and to provide optimum long wavelength recording, for example at the lateral edges of the record medium channel where the bias field intensity is more intense. The record medium 14 when associated with the embodiment of FIGS. 8-10 thus provides a tape with a recorded track having a gradient in its response characteristic from edge to edge of the tape with the low frequencies recorded substantially in an optimum manner at the lateral margins of the channel of the record tape and with the high frequency components for example in the megacycle range recorded substantially in an optimum manner at the central portion of the recorded channel. Such a recorded tape has a gradient in its long wavelength response with respect to the transverse direction and has a gradient in its short wavelength response with respect to the transverse direction at right angles to the direction of tape movement.

In FIG. 9, the tape engaging surface 2600 of the housing 260 is flush with the tape engaging surface 305 of pole 212 and flush with the tape engaging surface 216 of the pole 211.

As indicated in FIG. 10, suitable fastening elements 311- 314 are provided for securing the housing 260 to the head mounting blocks 241 and 242. For the sake of a definite example, screw-type fastening elements have been indicated in FIG. 6 at 312 and 313. The fastening elements 3l1-3l4 prevent head movement with respect to the keeper housing 260 in spite of temperature changes and the like.

With current flow in the ribbons 301 and 302 in the directions indicated by arrows 316 and 317, the ribbons 301 and 302 act jointly as a cross field in the same way as a single ribbon wrapped about both poles 211 and 212 together as in the aforementioned copending application Ser. No. 528,934 filed Feb. 21, 1966. With the current in ribbon 301 reversed from that shown by the arrow 316, the ribbons 301 and 302 (or one of the ribbons alone) acts as a signal coil or serves to produce a longitudinal component of bias frequency magnetic field, in place of supplying such bias frequency or signal current to the main winding 275, for example. The advantage of use of this configuration over a signal winding such as 275 lies in the fact that the conductors are close to the gap and give efficient coupling, especially at bias frequencies in the megacycle range.

The feature of FIG. 9A, taken in conjunction with FIGS. 8 and 10 are also applicable to any of the embodiments illustrated herein, but for convenience, the reference numerals and structure of FIG. 8 have been repeated in FIG. 9A. The housing 260 is identical to that illustrated in FIG. 10 except that the external surface 322 of the housing is somewhat below the level of the tape engaging surfaces 305 of pole 212 and 216 of pole 211. The edges of the successive turns of the ribbon 302 and of the ribbon 301 are flush with the surfaces 216 and 305 and follow the configuration of the poles 211 and 212 for a substantial distance along the tape path at each side of the gap between the poles. The keeper 260 which is also of a magnetically soft material may otherwise correspond identically to the housing 260 as illustrated in FIGS. 6 and 10, for example.

During polishing and in use of the heads such as illustrated in FIGS. 9 and 9A, the contour of the poles such as 212 at the tape engaging surface 305 and the upper edges of the ribbon conductors such as 302 become somewhat crowned as in dicated by dash lines 325 and 326, and this crowning is desirable to insure good tape contact. This is also true of the other embodiments herein; that is the core configurations as viewed in transverse cross section should actually show a certain degree of crowning or protrusion of the tape engaging surfaces at the region of the gap 13 or 213.

The location of the machine screw fasteners 311314 at the top surface of the keeper housing 260 maintain the head and keeper housing in accurate relation at the tape riding surfaces such as 260, 216 and 305 even with loose thread tolerances and allows differential expansion at the bottom between the head mounting blocks 241 and 242 and the housing 260. If the screws extend in a horizontal direction the thread tolerance could defeat the desired fixed accurate relationship between the tape engaging surfaces of the head and keeper housing.

In each of the embodiments the insulation between adjacent surfaces of the core part, that is the insulation between laminations such as indicated at 74 and between the laminations and the core parts such as 10b, 72 and 73 in FIG. 2B, for example, and between the core part 76a and 760 for example, in FIG. 2C, and also the nonhardening material such as indicated at 30 in FIG. 2, for example, should be very thin to give the lowest possible magnetic reluctance between the auxiliary and working core parts. A suitable insulation is magnesium oxide formed by decomposition of a magnesium methylate coating. The magnetic reluctance is also reduced by increasing the area of contact between the auxiliary and working parts, the construction of FIG. 2A, for example, giving about three times the confronting area at the regions indicated at 30a as compared to the area between the confronting surfaces at the region 30 in FIG. 2. Spot welding at one point, for example of part 25 to part 21 at the region 11, 21a in FIG. 1, also decreases reluctance while allowing freedom of movement to prevent stresses. This limited region spot welding of adjacent core parts preferably at a single location, is specifically disclosed with respect to each of the embodiments herein. The adjacent spot welded core parts may be in substantial contact over their entire confronting surfaces or may have a very thin layer of insulation and/or non hardening material therebetween.

Referring to the embodiment of FIGS. 4 and 5, by way of preferred example, the working core configuration 210 may have a width dimension of 18 mils (1 mil equals 0.001 inch), and depth dimension of 2 mils (corresponding to the thickness of the sheet material forming the working core an auxiliary parts 217 and 218). The auxiliary core parts 217 and 218 may have a width dimension of 24 mils and the same thickness dimension of 2 mils. As illustrated, the working core 210 and the auxiliary parts 217 and 218 may be formed from a single sheet of Supermalloy, having an initial width of the order of 78 mils before it is formed into the channel cross section shown in FIG. 5. The inner flanges such as 2170 and 218a may be of substantially semicircular configuration with a radius of curvature of 30 mils. The additional material 220 may be formed of laminations which are one-half mil thick Supermalloy and having a width dimension of the order of 14 mils, and formed into semicircular arcs-with radii varying from approximately 32 mils to 52 mils.

As a first example, two coils I turns each may link the respective core sections 231 and 232 which coils are connected in series for playback, and in parallel for recording operation. Alternatively only one of the 100 turn coils may be used for recording. As a second example, two coils may be utilized on the core sections 231 and 232 respectively, one having 100 turns for use during recording and the other coil having 400 turns for use alone during playback. As a third example a single coil such as indicated at 275 may be utilized having I000 turns which are all used for playback, the coil being tapped so that 50 turns, for example, may be utilized during recording.

As another example of dimensions, the working core a FIG. 2A, may have a width dimension'of mils, a thickness of 2 mils, and the legs 70a and 71a may have a width dimension of 24 mils. As an alternative example for FIG. 2A, the core parts 10a, 70a and 71a may be formed from a sheet of Superrnalloy having a thickness of 4 mils (01004 inch), the auxiliary core material 20a also being formed of Supermalloy.

Referring to the embodiment of 2M, the working core 10m may have a cross section 12 mils wide and 4 mils thick, while the legs 141 and 142 have a long cross-sectional dimension equal to about 22 mils.

In FIG. 2N, the working core 10n may have a width dimension of 8 mils and a thickness dimension of 4 mils with a very thin insulating layer therebetween as indicated at 325 for example of magnesium oxide as previously described. The legs 144 and 145 may have a long crosssectional dimension of 20 mils, for example. It will be noted that embodiments such as indicated in FIGS. 2M and 2N give increased thickness for the tape engaging surfaces such as 16m and 16n while avoiding grooves in such surface of the type which are required for a laminated configuration as indicated at 16k in FIG. 2K. Further, the configurations such as those of 2M and 2N require no cementing to hold them together after annealing, as is required with a laminated configuration such as indicated in FIG. 2K.

It should be noted that in each case where auxiliary low coercive force material is to be utilized, it must have a special heat treatment as will be well understood by those skilled in the art, and this is especially true of Supermalloy.

As a further specific example, the auxiliary core parts 20m in FIG. 2M are welded to the working core at a limited region preferably by means of a single .spotweld for each part and preferably in the region of the poles such as 11m of the working core.

Preferably each of the heads is of very small diameter to reduce the ratio of iron lengths to gap lengths, the entire head preferably being one-sixteenth inch to one-eighth inch in diameter or less. A head one thirty-second inch in diameter has been constructed. The magnetic material forming the signal flux paths of the core including the auxiliary material may have a grain direction or magnetic orientation at right angles to the signal flux path for minimum residual magnetization in the direction of the signal flux path. The working magnetic core parts may, for example, beof a magnetically soft ferrite material, while the auxiliary material is of a magnetically soft metal.

FIGS. 11, 12 and 13 illustrate a further embodiment particularly characterized in that pole 411 has its polar surface 416 spaced from the tape path by means of a nonmagnetic spacer 418 while the pole 412 has its polar surface 419 in sliding engagement with the magnetizable layer of the record tape 14 as in the previous embodiments. Electrically conductive gap spacer element 432 extends into the space between nonmagnetic material 418 and the pole 412 so as to provide at its upper edge a part of the tape engaging surface of the head in the same way as in the preceding embodiments. The nonmagnetic material 418 may have a tape engaging surface 418a which is crowned at the region of the gap, and the pole 412 may have its surface 419 similarly crowned, as was described in connection with the preceding embodiments.

The head configuration of FIGS. 1113 may incorporate any of the features of the preceding embodiments, but by way of example core sections 435 and 436 may be identical to core sections 231 and 232 of FIG. 4 and may include the horizontal lamination filler as seen in FIG. 5. An electrical signal winding is illustrated at 440 which may be of toroidal configuration and be associated with electrically conductive mounting blocks all as described in connection with FIGS. 5 and 6, for example. The keeper housing for the embodiment may be as illustrated in FIG. 9 or 9A and 10. Where the keeper housing is arranged as illustrated in FIG. 9, the keeper tape engaging surface 260a would be crowned and would conform in contour with the surfaces 418a and 419.

FIG. 12 is a diagrammatic view illustrating the gap spacer 432 before the same is folded into the configuration illustrated in FIG. 13. Connecting conductive ribbons are indicated at 444 and 445 which ribbons may lead to terminals at the bottom of the housing for the head assembly. The ribbons 444 and 445 lap end portions 432a and 432b of the gap spacer 432 and these end portions are shown as being folded against the core part 436 in FIG. 13. For illustrative purposes a source of high frequency bias current is indicated at 450 which may supply constant amplitude bias current in the megacycle range to the gap conductor 432 for establishing a component of bias frequency magnetic field between the pole 411 and the pole 412. Also for the purpose of diagrammatic illustration, a crossfield ribbon conductive winding 452 has been illustrated which is also shown as being energized at the bias frequency from source 450 so as to produce a cross field component of magnetic field between the keeper tape engaging surface such as diagrammatically indicated at 460a and the polar surfaces 416 and 419. The keeper surfaces 460a may be flush with the upper edges of the winding 452 and with the tape engaging surfaces 418a and 419, or the keeper surfaces 460a may be offset below the tape path and flush with the polar surface 416 in the manner indicated at 322 in FIG. 9A. The winding 452 may be provided by means of individual winding sections as indicated at FIG. 8 with the current flow directions indicated at 316 and 317 so as to produce a bias frequency magnetic field in the crossfield or transverse direction. Of course, the bias frequency current supplied to gap conductor 432 and to winding 452 may be suitably adjusted as to relative amplitude and phase so as to produce the optimum resultant bias frequency field as explained in my pending applications such as Ser. No. 528,934 filed Feb. 21, 1966 referred to above.

FIG. 11 indicates suitable recording amplifier circuitry at 470 and playback amplifier circuitry at 471 and shows switch means 472, 473 and 474 for connecting the circuitry to operate in various modes. For example with switch 472 in its upper position, recording current is superimposed on the bias frequency current and both are supplied to the gap conductor 432. With the switch 472 in the lower position, recording current from the circuitry 470 may be supplied to 100 turns of winding 440, for example. With switch 473 open and with switch 472 in an open or upper condition, the system may be conditioned for playback operation by closing switch 474 which may connect the entire winding 440 to the input of the playback circuit 471.

All of the features herein described may be applied to the system of FIGS. 11-13, and the features of FIGS. 11-13 may be applied to all of the other embodiments as will be apparent to those skilled in the art.

The material 418 may comprise a ceramic coating on the polar surface 416 and having a thickness from 0.0005 inch to 0.00005 inch. The gap spacer 432 may have a thickness from 0.0005 inch to 0.00005 inch. The core parts 435 and 436 may be formed with main core parts of 0.004 inch thick Supermalloy having an initial width of the order of 78 mils, but folded as indicated in FIG. 12 to provide a working core cross section of 18 mils by 4 mils thick and to provide auxiliary side legs such as indicated at 481 and 482 having a lengthwise cross-sectional dimension of the order of 20 mils with one-half mil Supermalloy laminations providing the auxiliary material 484. Alternatively, the auxiliary material 484 may be of solid cross section Supermalloy. Where the amplifier circuitry 470 provides a video signal with frequency components up to the megacycle range, 100 turns may be utilized for the recording section of winding 440. For playback of the, video signal, the winding 440 may have 300 turns, or individual winding sections on the core parts 435 and 436 may each have 100 turns and be connected in series to the playback circuitry 471 for playback, while one of the windings may be connected to the output of circuitry 470 during recording. The winding 440 would have fewer turns for operation with frequency components above approximately 3 megacycles per second. In a preferred mode of operation, the switch 472 would be in the upper position so that the recording current including frequency components above approximately 3 megacycles per second or at least in the megacycle range would be supplied to the crossfield conductor 432. The winding 440 would then be employed only for playback operation. Alternatively the gap spacer 432 could also be utilized during playback in conjunction with a step-up transformer.

FIG. 14 illustrates an embodiment wherein an especially small core configuration 500 may correspond to any of the core configurations herein disclosed and may have a toroidal winding as indicated at 501 for reproducing the higher frequency components of a recorded signal and supplying the same to an amplifier 502. A low frequency core part is indicated at 505 having a winding 506 for reproducing low frequency components of the recorded signal and supplying them to the amplifier 502. Still higher frequency components may be reproduced by a gap spacer of core 500 as in the embodiment of FIGS. l1-l3.

The tumin gap energization as by gap spacer 432 is espeeially advantageous where the working core is of a relatively thick material, while a multiturn coil such as indicated at 440 is advantageous for playback. Multitum coils can also be used to provide for four passes of a one-fourth inch tape (a total of 12 tracks, for example) giving an hour of color television recording or playback on a reel about 7 or 8 inches in diameter with extra thin tape.

Referring to FIG. 11, it is important to have a very accurate straight sharp edge at the junction of a pole 419 with the gap spacer 432 that is maintained through the life of the head. Spacer 432 should preferably be of the highest possible electrical conductivity. Beryllium copper provides a hardness that will maintain a sharp junction and yet has high conductivity. The pole piece 419 may be of Sendust, Alfenol, and the like to hold the sharp edge; and it is also advantageous to make this pole piece of high saturation magnetic material as previously indicated.

' The layer 418 may be of a glasslike material such as silicon monoxide which can be vapor deposited, quartz or porcelain enamel. The thickness of the separation layer 418 is of the same order as the thickness of the gap spacer 432. As an example, such thickness may be from about 0.001 inch to about 0.00002 inch for heads operating in the megacycle range, or

' for wave lengths of 0.0002 inch or less.

for signal current during recording in any of the embodiments,

with the high frequency bias for example in the megacycle range and above the highest frequency component to be recorded, supplied to the turn-in gap conductor such as 432. Where the head core has considerable core loss at the highest frequencies, the head may be utilized with a playback amplifier such as indicated at 471 having an especially high rate of rise at high frequencies in its response characteristic as a function of frequency.

Head units in accordance with any of the embodiments hereof may be utilized in the color television recording and playback system of my copending application Ser. No. 528,934 filed Feb. 21, I966 and of any of the applications referred to therein. The head unit dimensions may be such as Referring to the embodiment of FIG. 14, the small head 500 records both short and long wavelengths efficiently using any of the arrangements herein described; but does not playback the long wavelengths efficiently. In addition to the increased playback efficiency when the core 505 is used with its low frequency winding 506, the inefficient response of the small head 500 has the advantage of being innocuous to very short wavelength recordings on the tape. It has been found that sharp gap playback heads which are also efficient at long wavelengths have a tendency to concentrate the long wavelength magnetization picked up from the tape at the sharp gap and thus exert an erasing effect on the recorded short wavelengths. In the arrangement of FIG. 14 core 505 actually diverts this recorded long wave length flux from core 500 to avoid this erasing effect.

The material 418 may be a flame sprayed ceramic such as barium titanate, or stainless steel, or preferably chromium plate deposited on a pole surface 416 of Supermalloy or other material. To test the effectiveness of a head of the construction of FIGS. 4 and 5 a direct current was put through the windings, the current being approximately times greater than the maximum recording current used with this head during normal operation. No adverse effect was noticed on playback of short waves of about 0.00005 inch wavelength immediately after this current was removed, and the noise level did not increase. No adverse effect was noticed when the same test was made during recording. When heads of ordinary cons'truction were tested in this way, they erased the signal completely on previously recorded tapes and were inoperative or very noisy when used for recording.

The decrease in residual magnetization required for effective operation depending on the type of working core material, on its conditions of stress, on the sensitivity of the tape to such fields, on the criticality of the performance requirements with respect to noise and shortwave response, on the size and type of head gap, on the exposure to magnetizing conditions, etc. The preferred constructions described here allow the residual magnetization to be reduced to a value where it has no adverse effect on the tape under all operating conditions.

With respect to the embodiment of FIG. 2B, it will be understood that an alternative arrangement is to utilize the material connecting regions 81 and 82 as the working core material and to utilize such working core material to define the poles for coupling to the record medium. In this event the materiallO, would be the unstressed auxiliary material which would be out of contact with the record medium. In each of the embodiments, the auxiliary material is tapered in the region of the gap so that the pole faces have a cross section comparable to the cross section of the working core, although the poles may be ground down somewhat so that the pole end face such as seen at 212a in FIG. 9 and in FIG. 9A may have a reduced thickness in comparison to the normal thickness of the working core. In each of the embodiments, the tape record medium may have a width substantially greater than the maximum width of the head so as to be supported by the keeper surface such as 260a at each side of the aperture such as indicated at 290 in FIG. 10. Referring to FIG. 9A, even after the head configuration is substantially crowned as indicated at 325 and 326, the magnetizable surface of the record medium will still be spaced a substantial distance above the edges of the keeper housing such as indicated at 328 in FIG. 9A. This means that the record medium will not be exposed to the relatively intense field immediately at the edges such as 328, this field for example being a bias frequency field having a frequency in the megacycle range.

Referring to the offset pole feature of FIG. 11, in wide band recording applications it is a common experience that when microsize gaps are used, sen'ous disadvantages are encountered. During recording it is difficult or impossible to bias the tape adequately, and the head may saturate at recording levels well below the tape saturation level. During playback the head output voltage is low, and the signal to noise ratio is poor. If the recording density were greatly improved, the low output might be tolerated. However with very short gaps, the recording density turns out to be poorer than for larger gaps, at least with ordinary tapes. One is therefore forced to the conclusion that there is an optimum size of gap (engineering compromise), below which satisfactory operation may be unobtainable.

Where high frequency bias is used for recording, an inner boundary exists near the recording gap within which the bias field is so strong that ideally whatever recording takes place on one cycle is cancelled on the reverse cycle. Beyond this inner boundary, near the trailing pole there is a critical zone" where the recording is made. That is to say, the recording in effect actually takes place near the trailing pole of the head as the tape passes thereover. This happens because the tape retains only the magnetization acquired in the critical zone. However, ideal conditions seldom exist; and especially with low bias and strong signals, orwith biasless recording, certain wave lengths may be weakened or strengthened depending on gap and tape dimensions. For example, in the interval of time it takes for an increment of tape to transverse the recording gap region the flux can change such that some or all of the signal impressed on the tape prior to the critical zone is not cancelled, but is merely reduced or increased as it passes through the varying flux at the trailing pole in the critical zone.

On playback, nulls occur when the effective size of the head gap is an integral multiple of the recorded wavelengths, so that the signal is cancelled at high frequencies corresponding to short wavelengths. To overcome this problem fine gap heads of micron size must be used to prevent nulls within the operating frequency range, leading to the difficulties mentioned above.

The offset pole configuration of FIG. 11 overcomes the problems outlined above by providing a head construction which minimizes the deleterious effects of the leading pole of the magnetic head during recording and the null effect due to gap length during playback.

Each of the features described herein is specifically disclosed as being applied to each of the embodiments, and thedescription of each of the embodiments is specifically applied to each of the other embodiments to the extent not incon sistent with such other embodiments.

The head configurations disclosed herein may be utilized as erase heads as well as recording or playback heads.

The head units disclosed herein may be utilized in the embodiments of my prior applications Ser. No. 835,017 filed Aug. 20, 1959, Ser. No. 126,121 filed July 24, 1961, Ser. No. 344,075 filed Feb. 11, 1964, Ser. No. 389,021 filed Aug. 12, 1964, now U.S. Pat. No. 3,469,037 Ser. No. 401,832 filed Oct. 6, 1964, now U.S. Pat. No. 3,495,046, Ser. No. 407,402 filed Oct. 29, 1964,now U.S. Pat. No. 3,513,265, Ser. No. 439,340 filed Mar. 12, 1965, now U.S. Pat. No. 3,502,795, Ser. No. 456,192 filed May 17, 1965, now U.S. Pat. No. 3,449,528 Ser.

No. 493,271 filed Oct. 5. 1965, now U.S. Pat. No. 3,531,600, and the aforementioned application filed Feb. 21, 1966, and each of the head units disclosed herein is specifically applied to each of the recording and playback systems illustrated in said copending applications and the resulting systems are each specifically incorporated herein by reference.

For present commercial magnetic record tapes having acicular oxide particles and a coercivity of about 250 oersteds, the threshold value of residual magnetic field just sufficient to have a substantial detrimental effect on such a record tape is about 200 oersteds. Thus the auxiliary means of the present invention whether integral with the working core, or separate from the working core, or provided by both integral and separate core parts, is preferably constructed and arranged to reduce the maximum residual field intersecting the record medium path to a value less than about 200 oersteds. Preferably the auxiliary means provides such a reduction under all operating conditions to which the head may reasonably be expected to be subjected.

Commercial data shows that values of DC coercivity for commercially available Supermalloy (as measured from direct current saturation) may have a range from 0.003 to 0.009 oersted, and that commercial values of DC coercivity for 4-- 79 Permalloy may range from 0.02 to 0.07 oersted (as measured from direct current saturation). In designing a commercial head in accordance with the present invention to provide a residual field in the tape path of less than 200 oersteds, it may be necessary to take into account possible variations in direct current coercivity of commercially available materials and other such factors. It is the value of direct current coercivity rather than coercivity as measured with an applied AC field of a specified frequency which best indicates the merits of a material for the purpose of this invention.

It may be noted that an analysis of the design of a head such as shown in FIG. 1 may be approached by plotting magnetic flux CD as a function of magnetomotive force (mmf.) rather than as a function of magnetizing force H, as was done in FIG. 3. The mmf. between points 28 and 11 in core parts 25 must always be essentially equal to the mmf. between points 21b and 21a in core part 21 where these adjacent points are separated by a minimum reluctance path as is desirable.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

The nonhardening layers such as 30a and the insulating layers which may be substituted therefor to provide electrical isolation, but with low reluctance between the working core parts and the auxiliary core parts such as 20a, may have a thickness of the order of 1 micron (one millionth of a meter).

The back gaps such as 27 may be of minimum reluctance, with faces of core parts 21 and 22, and core parts 25 and 26 in abutting contacting engagement.

The maximum saturation density for Supermalloy may range from 6500 to 7800 gauss, and for 4-79 Permalloy may range from 6500 to 8000 gauss, in commercially available samples.

I claim as my invention:

1. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and

auxiliary means disposed adjacent said magnetic core'for diverting residual flux due to residual magnetization of the core from the path of the record medium,

said auxiliary means being essentially disconnected from the material forming said magnetic core so as to accommodate relative thermal expansion therebetween.

2. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and

auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium,

a relatively wide sheet of magnetic material having a first portion of the width thereof defining said magnetic core and having a second portion of the width thereof defining said auxiliary means,

said second portion of said sheet being joinedwith said first portion by means of a bend to offset said second portion from the level of the first portion.

3. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and

auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium,

said magnetic core having a signal flux path therein and the material of said magnetic core being oriented generally at right angles to said signal flux path.

4. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and

auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium,

a keeper housing containing said core and said auxiliary means and having a top surface adjacent the record medium path,

mounting means for holding the core, and

fastening means at the top surface of the housing securing the housing to the mounting means and exerting fastening force generally normal to the top surface of the housing 5. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and

auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of v the core from the path of the record. medium,

said auxiliary means being a separate piece of material from said magnetic core and having a magnetic length substantially less than said magnetic core and a cross section substantially greater than that of said core.

6. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the redium, said auxiliary means being in a substantially unstressed condition, said magnetic core having a signal flux path therein and having a cross-sectional configuration transverse to said signal flux path with an interior space, and said auxiliary means comprising auxiliary magnetic material disposed within said interior space of said magnetic core, the material of said magnetic core extending on three sides of the auxiliary magnetic material within said interior space.

7. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being in a substantially unstressed condition, said auxiliary means in its entirety being spaced from the record medium path so as to be "lear of contact with the magnetic record medium, said magnetic core having confronting poles with upper record contacting surfaces for sliding engagement with the record medium, the coupling means comprising a nonmagnetic gap between the poles, and the poles having under surfaces opaosite the upper record contacting surfaces thereof, and said .;.uxiliary means comprising auxiliary material extending along the under surfaces of the poles and having a substantially greater thickness dimension than the thickness dimension of the poles between the under surfaces and the upper record tontacting surfaces thereof.

8. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being in a substantially unstressed condition, said auxiliary means being formed in the same magnetic material and integral with said magnetic core and said magnetic core having adequate flux carrying capacity for efficient recording operation without said auxiliary means, and said auxiliary means having a cross section substantially greater than the cross section of said magnetic core and serving to reduce the field due to residual magnetization of said magnetic core which intersects the record medium path to a value substantially below the coercivity of the record medium.

9. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being in a substantially unstressed condition, said auxiliary means reducing the residual flux which intersects the record medium path by at least 50 percent in comparison with the case where the auxiliary means is omitted, said magnetic. core having confronting poles with upper record contacting surfaces for sliding engagement with the record medium, the coupling means comprising a nonmagnetic gap between the poles, and the poles having under surfaces opposite the upper record contacting surfaces thereof, and said auxiliary means comprising auxiliary material extending along the under surfaces of the poles and having a substantially greater thickness dimension than the thickness dimension of the poles between the under surfaces and the upper record contacting surfaces thereof, said auxiliary material being within a distance of not greater than about 0.00l inch of said magnetic core, but being entirely clear of the region between said poles.

10. A magnetic head for coupling to a track on a magnetic record medium and having a predetermined scanning width corresponding to the width of said track, said head comprising a magnetic core having coupling means for coupling the magnetic core to said track as the record medium travels along a record medium path across said core,

a relatively wide sheet of magnetic material having a first portion of the width thereof forming said magnetic core and having a second portion of the width of said sheet substantially increasing the flux carrying capacity of the head without increasing the scanning width thereof, said first portion of the width of said sheet having a width dimension defining the scanning width of the head, and

auxiliary means comprising said second portion of said sheet and providing magnetic material having a coercivity substantially lower than the coercivity of the magnetic core for diverting residual flux due to residual magnetization of the magnetic core from the path of the record medium.

11. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition, said magnetic core comprising a core portion adjacent said coupling means and across which the record medium travels, and said auxiliary means comprising an integral lateral extension of said core portion and extending on the side of said core portion remote from the record medium path.

12. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition, said magnetic core having a generally channel cross section to define a pocket on the side of the core remote from the record medium path, and said auxiliary means comprising separate pieces of magnetic material disposed inside said pocket.

13. A magnetic head for coupling to a magnetic record medium comprising a magnetic core having a plurality of individual core parts of sheet magnetic material defining a magnetic circuit having a region for coupling to a magnetic record medium, at least one of said core parts having a body portion with a width dimension between opposite side margins extending generally transversely to the path of magnetic flux through said one of said core parts and having an integral angularly related portion extending at a substantial angle from at least one side margin of said body portion for increasing the cross-sectional area of the portion of the magnetic circuit defined by said one of said core parts without a corresponding increase in the width dimension of the core part.

14. A magnetic head for coupling to a magnetic record medium comprising a magnetic core having a plurality of core parts of sheet magnetic material defining a magnetic circuit having a region for coupling to a magnetic record medium, said core parts having a channel section transverse to the flux path through said parts throughout a substantial portion of the length thereof.

15. A magnetic head for coupling to a magnetic record medium comprising a magnetic core having a plurality of core parts of sheet magnetic material defining a magnetic circuit having a region for coupling to a magnetic record medium, said core parts having a channel cross section transverse to the flux path through said parts throughout a substantial portion of the length thereof but having a rectangular cross section adjacent said region for coupling to the record medium to provide reduced cross section pole portions.

16. A magnetic head comprising a magnetic core having a signal flux path therein of loop configuration and having coupling means for coupling the signal flux path of the magnetic core to a magnetic record medium traveling along a record medium path, auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition as finally assembled, said magnetic core having an elongated side face thereof which defines a boundary of the signal fiux path in said magnetic core and said elongated side face extending over substantially the entire length of said signal flux path in said magnetic core, said auxiliary means comprising separate auxiliary magnetic material formed entirely separately from the magnetic core and said separate auxiliary magnetic material having an elongated surface thereof disposed in confronting relation to said elongated side face of said magnetic core material over substantially the entire length of said elongated side face, said auxiliary magnetic material having a substantial cross-sectional area in comparison to the cross-sectional area of saidmagnetic core so as to provide substantial additional flux carrying capacity parallel to said signal flux path, and an electric winding encircling in common the signal flux path of said magnetic core and said separate auxiliary magnetic material.

17. A magnetic head having a pair of poles, means providing a path for a magnetic record medium successively across said poles, one of said poles being disposed directly at the record medium path and the other of said poles being substantially offset from said record medium path and a nonmagnetic material interposed between the other of said poles and said record medium and having a thickness dimension of the order of 0.0005 inch.

18. The head of claim 17 with said nonmagnetic material being plated on said other of said poles.

19. A magnetic head having a pair of poles, means providing a path for a magnetic record medium successively across said poles, one of said poles being disposed directly at the record medium path and the other of said poles being substantially offset from said record medium path, and the other of the poles being offset from the record medium path by a distance in the range from about 0.001 inch to 0.00002 inch.

20. The head of claim 19 with said other pole having a spacer of chromium plated thereon to provide said offset, with said record medium being in sliding contact with said spacer as it travels along said record medium path.

21. A magnetic head comprising a magnetic core having a signal flux path therein of loop configuration and having coupling means for coupling the signal flux path of the magnetic core to a magnetic record medium traveling along a record medium path, auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition as finally assembled, said magnetic core having an elongated side face thereof which defines a boundary of the signal flux path in said magnetic core and said elongated side face extending over substantially the entire length of said signal flux path in said magnetic core, said auxiliary means comprising auxiliary magnetic material having an elongated surface thereof disposed in confronting relation to said elongated side face of said magnetic core over substantially the entire length of said face, said auxiliary means in its entirety being spaced from the record medium path so as to be clear of contact with the magnetic record medium and having a cross-sectional area at least approximately equal to the cross-sectional area of said magnetic core to add substantially to the flux carrying capacity of the magnetic core without substantially increasing the scanning width of the magnetic head,

- and an electric winding encircling in common the signal flux path of said magnetic core and said auxiliary magnetic material.

22. A magnetic head according to claim 21 with the magnetic core being formed of magnetic material which is in an unstressed condition compared to laminations which are glued and clamped after anneal.

23. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition, said magnetic core having magnetic core material defining a loop magnetic flux path for coupling with the magnetic record medium at said coupling means, said magnetic corematerial providing at an outer side of the loop magnetic flux path an outer elongated side face which slidably engages with the magnetic record medium adjacent said coupling means, and providing at an inner side of the loop magnetic flux path opposite said outer side an inner elongated side face, said auxiliary means of magnetic material comprising auxiliary magnetic material of sheet configuration disposed substantially at right angles to said inner elongated side face of said magnetic core and extending along said inner elongated side face over substantially the entire length thereof, said auxiliary magnetic material having a cross section at least substantially equal to the cross section of said magnetic core material, said auxiliary means in its entirety being spaced from the record medium path so as to be clear of contact with the magnetic record medium, said auxiliary magnetic material serving to substantially add to the flux carrying capacity of the magnetic core without increasing the scanning width of the magnetic head, and an electric signal winding coupled in common to said signal flux path of said magnetic core material and said auxiliary magnetic material.

24. A magnetic head in accordance with claim 23 with said magnetic core material being in an unstressed condition compared to laminations which are glued and clamped after anmeal.

25. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, mounting means secured to said magnetic core for fixedly positioning the same relative to said record medium path during a transducing operation, and

said mounting means being spaced from said auxiliary means by a nonrigid medium so as to avoid stressing of the material of said auxiliary means.

26. The head of claim 25 with said auxiliary material being integral with said magnetic core, and the space between said auxiliary means and said mounting means being filled with a yieldable material.

27. The head of claim 25 with said auxiliary means being separated from said magnetic core by a layer of nonrigid medium.

28. The head of claim 27 with said auxiliary means being spot welded to said core at the part thereof near said coupling means.

29. The head of claim 27 with said layer having a thickness dimension of not greater than about 0.001 inch over at least a substantial proportion of the area thereof.

30. A magnetic head comprising a magnetic core having a coupling gap for coupling ofthe core with a magnetic record medium moving along a record medium path across the core, said magnetic core being formed of relatively wide sheet material.

said sheet material having confronting free end portions of reduced width at opposite sides of said coupling gap, said sheet material providing a loop magnetic flux path between said free end portions for magnetic flux interlinkage with the record medium at said coupling gap, said free end portions having a width dimension extending along the transverse boundaries of said coupling gap corresponding to the width of the channel of the record medium to which said magnetic core is coupled,

said sheet material providing a main magnetic core portion extending along said loop magnetic flux path and having a width equal to the width dimension of said free end portions,

said sheet material providing an auxiliary magnetic core portion for diverting residual flux due to residual magnetization of the core from the path of the record medium, and extending laterally from the main core portion to provide a total width of said sheet material transverse to said loop magnetic flux path except at said free end portions which total width is substantially greater than the width dimension of said free end portions at the transverse boundaries of said coupling gap,

said auxiliary magnetic core portion being spaced from the record medium path over its entire extent so as to be clear of contact with the record medium, and

auxiliary means comprising said auxiliary magnetic core portion for reducing the field intersecting the record medium path due to a maximum residual magnetization of the magnetic core to a value substantially below the coercivity of the record medium.

31. A magnetic transducer head according to claim 30 with said auxiliary magnetic core portion of thewidth of said sheet material having a lateral dimension at least substantially equal to the width dimension of said main magnetic core portion so that the total width of said sheet material is at least substantially twice the width dimension of said main magnetic core portion.

32. A magnetic transducer head according to claim 30 with said'auxiliary magnetic core portion of the width of said sheet material providing a residual magnetic flux path for residual flux produced by residual magnetization of said main core portion bypassing said record medium and serving to reduce the residual flux intersecting the record medium path by at least about 50 percent compared with a head consisting of said main magnetic core portion only.

33. A magnetic transducer head according to claim 30 with said auxiliary magnetic core portion of said sheet material having a cross section substantially greater than that of said main magnetic core portion of said sheet material.

34. A magnetic transducer head according to claim 30 with said auxiliary means being further provided by auxiliary magnetic material disposed adjacent to but insulated from said sheet material on the side thereof away from said record medium path.

35 A ma netic transducer head according to claim 34 with said auxl iary magnetic material having a coercivity as measured from direct current saturation not substantially greater than from 0.003 oersted to 0.009 oersted. 

1. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being essentially disconnected from the material forming said magnetic core so as to accommodate relative thermal expansion therebetween.
 2. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, a relatively wide sheet of magnetic material having a first portion of the width thereof defining said magnetic core and having a second portion of the width thereof defining said auxiliary means, said second portion of said sheet being joined with said first portion by means of a bend to offset said second portion from the Level of the first portion.
 3. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said magnetic core having a signal flux path therein and the material of said magnetic core being oriented generally at right angles to said signal flux path.
 4. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, a keeper housing containing said core and said auxiliary means and having a top surface adjacent the record medium path, mounting means for holding the core, and fastening means at the top surface of the housing securing the housing to the mounting means and exerting fastening force generally normal to the top surface of the housing
 5. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being a separate piece of material from said magnetic core and having a magnetic length substantially less than said magnetic core and a cross section substantially greater than that of said core.
 6. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the redium, said auxiliary means being in a substantially unstressed condition, said magnetic core having a signal flux path therein and having a cross-sectional configuration transverse to said signal flux path with an interior space, and said auxiliary means comprising auxiliary magnetic material disposed within said interior space of said magnetic core, the material of said magnetic core extending on three sides of the auxiliary magnetic material within said interior space.
 7. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being in a substantially unstressed condition, said auxiliary means in its entirety being spaced from the record medium path so as to be clear of contact with the magnetic record medium, said magnetic core having confronting poles with upper record contacting surfaces for sliding engagement with the record medium, the coupling means comprising a nonmagnetic gap between the poles, and the poles having under surfaces opposite the upper record contacting surfaces thereof, and said auxiliary means comprising auxiliary material extending along the under surfaces of the poles and having a substantially greater thickness dimension than the thickness dimension of the poles between the under surfaces and the upper record contacting surfaces thereof.
 8. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being in a substantially unstressed condition, said auxiliaRy means being formed in the same magnetic material and integral with said magnetic core and said magnetic core having adequate flux carrying capacity for efficient recording operation without said auxiliary means, and said auxiliary means having a cross section substantially greater than the cross section of said magnetic core and serving to reduce the field due to residual magnetization of said magnetic core which intersects the record medium path to a value substantially below the coercivity of the record medium.
 9. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, said auxiliary means being in a substantially unstressed condition, said auxiliary means reducing the residual flux which intersects the record medium path by at least 50 percent in comparison with the case where the auxiliary means is omitted, said magnetic core having confronting poles with upper record contacting surfaces for sliding engagement with the record medium, the coupling means comprising a nonmagnetic gap between the poles, and the poles having under surfaces opposite the upper record contacting surfaces thereof, and said auxiliary means comprising auxiliary material extending along the under surfaces of the poles and having a substantially greater thickness dimension than the thickness dimension of the poles between the under surfaces and the upper record contacting surfaces thereof, said auxiliary material being within a distance of not greater than about 0.001 inch of said magnetic core, but being entirely clear of the region between said poles.
 10. A magnetic head for coupling to a track on a magnetic record medium and having a predetermined scanning width corresponding to the width of said track, said head comprising a magnetic core having coupling means for coupling the magnetic core to said track as the record medium travels along a record medium path across said core, a relatively wide sheet of magnetic material having a first portion of the width thereof forming said magnetic core and having a second portion of the width of said sheet substantially increasing the flux carrying capacity of the head without increasing the scanning width thereof, said first portion of the width of said sheet having a width dimension defining the scanning width of the head, and auxiliary means comprising said second portion of said sheet and providing magnetic material having a coercivity substantially lower than the coercivity of the magnetic core for diverting residual flux due to residual magnetization of the magnetic core from the path of the record medium.
 11. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition, said magnetic core comprising a core portion adjacent said coupling means and across which the record medium travels, and said auxiliary means comprising an integral lateral extension of said core portion and extending on the side of said core portion remote from the record medium path.
 12. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition, said magnetic core having a generally channel cross section to define a pocket on the side of the core remote from the record medium path, and said auxiliary means comprising separate pieces of magnetic material disposed inside said pocket.
 13. A magnetic head for coupling to a magnetic record medium comprising a magnetic core having a plurality of individual core parts of sheet magnetic material defining a magnetic circuit having a region for coupling to a magnetic record medium, at least one of said core parts having a body portion with a width dimension between opposite side margins extending generally transversely to the path of magnetic flux through said one of said core parts and having an integral angularly related portion extending at a substantial angle from at least one side margin of said body portion for increasing the cross-sectional area of the portion of the magnetic circuit defined by said one of said core parts without a corresponding increase in the width dimension of the core part.
 14. A magnetic head for coupling to a magnetic record medium comprising a magnetic core having a plurality of core parts of sheet magnetic material defining a magnetic circuit having a region for coupling to a magnetic record medium, said core parts having a channel section transverse to the flux path through said parts throughout a substantial portion of the length thereof.
 15. A magnetic head for coupling to a magnetic record medium comprising a magnetic core having a plurality of core parts of sheet magnetic material defining a magnetic circuit having a region for coupling to a magnetic record medium, said core parts having a channel cross section transverse to the flux path through said parts throughout a substantial portion of the length thereof but having a rectangular cross section adjacent said region for coupling to the record medium to provide reduced cross section pole portions.
 16. A magnetic head comprising a magnetic core having a signal flux path therein of loop configuration and having coupling means for coupling the signal flux path of the magnetic core to a magnetic record medium traveling along a record medium path, auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition as finally assembled, said magnetic core having an elongated side face thereof which defines a boundary of the signal flux path in said magnetic core and said elongated side face extending over substantially the entire length of said signal flux path in said magnetic core, said auxiliary means comprising separate auxiliary magnetic material formed entirely separately from the magnetic core and said separate auxiliary magnetic material having an elongated surface thereof disposed in confronting relation to said elongated side face of said magnetic core material over substantially the entire length of said elongated side face, said auxiliary magnetic material having a substantial cross-sectional area in comparison to the cross-sectional area of said magnetic core so as to provide substantial additional flux carrying capacity parallel to said signal flux path, and an electric winding encircling in common the signal flux path of said magnetic core and said separate auxiliary magnetic material.
 17. A magnetic head having a pair of poles, means providing a path for a magnetic record medium successively across said poles, one of said poles being disposed directly at the record medium path and the other of said poles being substantially offset from said record medium path and a nonmagnetic material interposed between the other of said poles and said record medium and having a thickness dimension of the order of 0.0005 inch.
 18. The head of claim 17 with said nonmagnetic material being plated on said other of said poles.
 19. A magnetic head having a pair of poles, means providing a path for a magnetic record medium successively across said poles, one of said poles being disposed directly at the record medium path and the other of said poles being substantially offset from said record medium path, and the other of the poles being offset from the record medium path by a distance in the range from about 0.001 inch to 0.00002 inch.
 20. The head of claim 19 with said other pole having a spacer of chrOmium plated thereon to provide said offset, with said record medium being in sliding contact with said spacer as it travels along said record medium path.
 21. A magnetic head comprising a magnetic core having a signal flux path therein of loop configuration and having coupling means for coupling the signal flux path of the magnetic core to a magnetic record medium traveling along a record medium path, auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition as finally assembled, said magnetic core having an elongated side face thereof which defines a boundary of the signal flux path in said magnetic core and said elongated side face extending over substantially the entire length of said signal flux path in said magnetic core, said auxiliary means comprising auxiliary magnetic material having an elongated surface thereof disposed in confronting relation to said elongated side face of said magnetic core over substantially the entire length of said face, said auxiliary means in its entirety being spaced from the record medium path so as to be clear of contact with the magnetic record medium and having a cross-sectional area at least approximately equal to the cross-sectional area of said magnetic core to add substantially to the flux carrying capacity of the magnetic core without substantially increasing the scanning width of the magnetic head, and an electric winding encircling in common the signal flux path of said magnetic core and said auxiliary magnetic material.
 22. A magnetic head according to claim 21 with the magnetic core being formed of magnetic material which is in an unstressed condition compared to laminations which are glued and clamped after anneal.
 23. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means of magnetic material disposed adjacent said magnetic core and being in a relatively unstressed condition, said magnetic core having magnetic core material defining a loop magnetic flux path for coupling with the magnetic record medium at said coupling means, said magnetic core material providing at an outer side of the loop magnetic flux path an outer elongated side face which slidably engages with the magnetic record medium adjacent said coupling means, and providing at an inner side of the loop magnetic flux path opposite said outer side an inner elongated side face, said auxiliary means of magnetic material comprising auxiliary magnetic material of sheet configuration disposed substantially at right angles to said inner elongated side face of said magnetic core and extending along said inner elongated side face over substantially the entire length thereof, said auxiliary magnetic material having a cross section at least substantially equal to the cross section of said magnetic core material, said auxiliary means in its entirety being spaced from the record medium path so as to be clear of contact with the magnetic record medium, said auxiliary magnetic material serving to substantially add to the flux carrying capacity of the magnetic core without increasing the scanning width of the magnetic head, and an electric signal winding coupled in common to said signal flux path of said magnetic core material and said auxiliary magnetic material.
 24. A magnetic head in accordance with claim 23 with said magnetic core material being in an unstressed condition compared to laminations which are glued and clamped after anneal.
 25. A magnetic head comprising a magnetic core having coupling means for coupling the core to a magnetic record medium traveling along a record medium path, and auxiliary means disposed adjacent said magnetic core for diverting residual flux due to residual magnetization of the core from the path of the record medium, mounting means secured to said magnetic core for fixedly positioning the same relative to said record mediUm path during a transducing operation, and said mounting means being spaced from said auxiliary means by a nonrigid medium so as to avoid stressing of the material of said auxiliary means.
 26. The head of claim 25 with said auxiliary material being integral with said magnetic core, and the space between said auxiliary means and said mounting means being filled with a yieldable material.
 27. The head of claim 25 with said auxiliary means being separated from said magnetic core by a layer of nonrigid medium.
 28. The head of claim 27 with said auxiliary means being spot welded to said core at the part thereof near said coupling means.
 29. The head of claim 27 with said layer having a thickness dimension of not greater than about 0.001 inch over at least a substantial proportion of the area thereof.
 30. A magnetic head comprising a magnetic core having a coupling gap for coupling of the core with a magnetic record medium moving along a record medium path across the core, said magnetic core being formed of relatively wide sheet material, said sheet material having confronting free end portions of reduced width at opposite sides of said coupling gap, said sheet material providing a loop magnetic flux path between said free end portions for magnetic flux interlinkage with the record medium at said coupling gap, said free end portions having a width dimension extending along the transverse boundaries of said coupling gap corresponding to the width of the channel of the record medium to which said magnetic core is coupled, said sheet material providing a main magnetic core portion extending along said loop magnetic flux path and having a width equal to the width dimension of said free end portions, said sheet material providing an auxiliary magnetic core portion for diverting residual flux due to residual magnetization of the core from the path of the record medium, and extending laterally from the main core portion to provide a total width of said sheet material transverse to said loop magnetic flux path except at said free end portions which total width is substantially greater than the width dimension of said free end portions at the transverse boundaries of said coupling gap, said auxiliary magnetic core portion being spaced from the record medium path over its entire extent so as to be clear of contact with the record medium, and auxiliary means comprising said auxiliary magnetic core portion for reducing the field intersecting the record medium path due to a maximum residual magnetization of the magnetic core to a value substantially below the coercivity of the record medium.
 31. A magnetic transducer head according to claim 30 with said auxiliary magnetic core portion of the width of said sheet material having a lateral dimension at least substantially equal to the width dimension of said main magnetic core portion so that the total width of said sheet material is at least substantially twice the width dimension of said main magnetic core portion.
 32. A magnetic transducer head according to claim 30 with said auxiliary magnetic core portion of the width of said sheet material providing a residual magnetic flux path for residual flux produced by residual magnetization of said main core portion bypassing said record medium and serving to reduce the residual flux intersecting the record medium path by at least about 50 percent compared with a head consisting of said main magnetic core portion only.
 33. A magnetic transducer head according to claim 30 with said auxiliary magnetic core portion of said sheet material having a cross section substantially greater than that of said main magnetic core portion of said sheet material.
 34. A magnetic transducer head according to claim 30 with said auxiliary means being further provided by auxiliary magnetic material disposed adjacent to but insulated from said sheet material on the side thereof away from said record medium pAth.
 35. A magnetic transducer head according to claim 34 with said auxiliary magnetic material having a coercivity as measured from direct current saturation not substantially greater than from 0.003 oersted to 0.009 oersted. 